1. Field of the Invention
The present invention, in general, relates to an induction heating apparatus and, more particularly, relates to an induction heating apparatus using a single-ended push-pull (SEPP) inverter.
2. Description of the Prior Art
Conventionally, as a driver circuit for this kind of induction heating cooking apparatus, a circuit in which a series resonance circuit comprised of an induction heating coil and a resonance capacitor is employed so that a high frequency inverter is structured by connecting a switching element in series with the resonance capacitor, is known. In such a cooking apparatus with the above described structure, an oscillation frequency of the inverter changes depending on an on interval of the switching element and a resonance cycle of the above described series resonance circuit. An input to a load is adjusted based on the change of the frequency, particularly, by controlling the on interval of the switching element. In such a cooking apparatus of the frequency control system type, a problem of noise generation arises when the cooking apparatus is of a multiunit structure. More particularly, if and when adjoining heating units are simultaneously operated, as a matter of course, an oscillation frequency of an inverter changes due to a difference of material of a pan to be heated or a difference of a set input. The above described noise is generated by mutual interference of the magnetic field from each heating unit and according to the frequency difference between both, and tends to become larger as the frequency difference becomes larger. Such noise generation causes a value of commodity to be lowered since it makes a user feel unpleasant.
Accordingly, if it is possible to control an input to a load, that is, an output, without changing an oscillation frequency of inverters, any audible noise caused by the frequency difference between each unit will not be generated even if an induciton heating apparatus comprises a plurality of heating portions or units. The present invention is achieved in consideration of this respect.